U.S. patent number 6,244,982 [Application Number 09/314,732] was granted by the patent office on 2001-06-12 for hydraulic chain tensioner with a piston having a plurality of sliding elements.
This patent grant is currently assigned to MorseTEC Europe S.p.A.. Invention is credited to Roberto Merelli.
United States Patent |
6,244,982 |
Merelli |
June 12, 2001 |
Hydraulic chain tensioner with a piston having a plurality of
sliding elements
Abstract
A hydraulic tensioning device for a power transmission system
having a belt or a chain includes a cylinder and piston assembly of
which a movable element, generally the piston, acts on the belt or
chain so as to ensure that it is tensioned and thus ensures taking
up of any slack in the chain or belt. The piston includes a
plurality of piston elements slidable along a central axis of the
cylinder.
Inventors: |
Merelli; Roberto (Monza Milan,
IT) |
Assignee: |
MorseTEC Europe S.p.A. (Milan,
IT)
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Family
ID: |
8236779 |
Appl.
No.: |
09/314,732 |
Filed: |
May 18, 1999 |
Foreign Application Priority Data
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Sep 9, 1998 [EP] |
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98830527 |
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Current U.S.
Class: |
474/138; 188/277;
188/302; 474/110; 74/579R |
Current CPC
Class: |
F16H
7/08 (20130101); F16H 2007/0806 (20130101); F16H
2007/0859 (20130101); Y10T 74/2142 (20150115) |
Current International
Class: |
F16H
7/08 (20060101); F16H 007/12 (); F16H 007/22 () |
Field of
Search: |
;474/110,111,138
;74/579R,579E ;141/354 ;188/277,299 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0039586 |
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Nov 1981 |
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EP |
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2320470 |
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Mar 1977 |
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FR |
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2113331 |
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Aug 1983 |
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GB |
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2203817 |
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Oct 1988 |
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GB |
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2093150 |
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Aug 1982 |
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GR |
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Other References
European Search report, EP 98 83 0527.2, dated 02/24/99..
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Primary Examiner: Luong; Vinh T.
Attorney, Agent or Firm: Fitch, Even, Tabin & Flannery
Dziegielewski; Greg
Claims
What is claimed is:
1. A hydraulic tensioner for a power transmission system
comprising:
a cylinder and piston assembly, said cylinder having an inner
chamber, said piston assembly slidably received within said inner
chamber, said piston assembly movable between a retracted position
and an extended position along a central axis of said cylinder,
said piston assembly further adapted to operate to tension said
power transmission system,
a source of pressurized fluid in fluid communication with said
inner chamber of said cylinder,
a piston spring located between said inner chamber and said piston
assembly, said pressurized fluid and said spring biasing said
piston assembly in an extending direction from said cylinder,
said piston assembly including at least two piston elements, each
of said piston elements being slidable along said central axis of
said cylinder, and at least one of said piston elements having a
passage extending therethrough.
2. A tensioner according to claim 1, wherein said piston elements
further comprise a distal element and a proximal element, said
distal and proximal elements being telescopically slidable with
respect to one another.
3. A tensioner according to claim 1, wherein said piston elements
are cylindrical in shape, said elements include a plurality of
spring rings disposed thereon and corresponding grooves formed
therein which limit the extension of said distal element with
respect to said proximal element, said rings and corresponding
grooves restricting the extension of at least one of said piston
elements with respect to said cylinder.
4. A tensioner according to claim 2, wherein each said piston
element includes a skirt portion having an inner and an outer
surface, a spring ring located on said outer surface of each
respective skirt portion, grooves being provided on the facing of
said inner surfaces of one of said piston elements and of said
cylinder.
5. A tensioner according to claim 4, wherein each said groove has a
steep distal circumferential wall and a gently sloping proximal
circumferential wall.
6. A tensioner according to claim 1, wherein said first piston
element is provided with a piston head and a skirt operatively
connected therewith, said second piston element comprising a skirt
in sealing relation with said cylinder, and said first piston
element disposed within said second piston element in a
telescopically slidable relation.
7. A tensioner according to claim 6, wherein said skirt of said
second piston element is in sealing relation with said first piston
element forming a generally continuous fluid chamber therein for
said pressurized fluid when said first piston element is extended
from said cylinder.
8. A tensioner according to claim 7, wherein said second piston
element forms said fluid chamber when said first piston element is
fully extended beyond said cylinder.
9. A hydraulic tensioner for a power transmission system
comprising:
a cylinder and piston assembly, said cylinder having an inner
chamber, said piston assembly slidably received within said inner
chamber, said piston assembly movable between a retracted position
and an extended position along a central axis of said cylinder,
said piston assembly further adapted to operate to tension said
power transmission system,
a source of pressurized fluid in fluid communication with said
inner chamber of said cylinder,
a piston spring located between said inner chamber and said piston
assembly, said pressurized fluid and said spring biasing said
piston assembly in an extending direction from said cylinder,
said piston assembly including at least two piston elements,
including a distal element and a proximal element, said distal and
proximal elements being telescopically slidable with respect to one
another,
said distal element and said proximal element including a skirt
portion having an inner and an outer surface, a spring ring located
on said outer surface of each respective skirt portion, grooves
being provided on the facing of said inner surfaces of one of said
piston elements and of said cylinder,
each of said grooves having a steep distal circumferential wall and
a gently sloping proximal circumferential wall.
Description
BACKGROUND OF THE INVENTION
This invention relates to hydraulic tensioners used as a control
device for a power transmission chain drive in automotive timing
applications and more particularly to a hydraulic tensioner having
a long maximum useful stroke, while having a normal cylinder-piston
assembly length in the retracted state.
A tensioning device, such as a hydraulic tensioner, is used as a
control device for a power transmission chain, or similar power
transmission device, as a chain travels between a plurality of
sprockets. As a chain transmits power from a driving sprocket to a
driven sprocket, one portion or strand of the chain between the
sprockets will be tight while the other portion of the chain will
be slack. In order to impart and maintain a certain degree of
tension in the slack portion of the chain, a hydraulic tensioner
provides a piston that presses against a tensioner arm or other
chain guiding mechanism.
Prevention of excess slack in the chain is particularly important
in the case of a chain driven camshaft in an internal combustion
engine because a chain without sufficient tension can skip a tooth
or otherwise throw off the camshaft timing, possibly causing damage
or rendering the engine inoperative. However, in the harsh
environment of an internal combustion engine, various factors can
cause fluctuations in the chain tension.
For instance, wide variations in temperature and thermal expansion
coefficients among the various parts of the engine can cause the
chain tension to vary between excessively high or low levels.
During prolonged use, wear to the components of the power
transmission can cause a decrease in chain tension. In addition,
camshaft and crankshaft induced torsional vibrations cause
considerable variations in chain tension. Reverse rotation of an
engine, occurring for example in stopping or in failed attempts at
starting, can also cause fluctuations in chain tension. For these
reasons, a mechanism such as a hydraulic tensioner is desired to
ensure the necessary tension on the slack side of the chain.
Typically, a hydraulic tensioner includes a piston in the form of a
hollow cylinder. The piston slides within a bore in the housing and
is biased outward from the housing in the direction of the
tensioner arm and chain by a piston spring. The interior of the
piston forms a high pressure fluid chamber with the bore or opening
in the housing. The high pressure chamber is connected through a
one way check valve to a low pressure chamber or reservoir, which
provides or is connected to an exterior source of hydraulic
fluid.
Upon start-up, the force of the spring on the piston causes the
piston to move further outward as the chain begins to move. Outward
movement of the piston creates a low pressure condition in the high
pressure fluid chamber, or pressure differential across the inlet
check valve. Accordingly, the inlet check valve opens and permits
the flow of fluid from the reservoir, or low pressure chamber, into
the high pressure chamber. When the high pressure chamber is
sufficiently filled with fluid, the force on the chain that moves
the piston inward will be balanced by the outward force from the
spring and the resistance force of the fluid in the chamber. The
force of the chain against the fluid in the chamber also causes the
check valve to close, which prevents further addition of fluid to
the chamber.
U.S. Pat. No. 4,826,470 to Breon et al. discloses a cylinder/piston
assembly tensioning device, in which the cylinder forms a chamber
for pressurized fluid. A static plunger is interposed between the
cylinder and the piston, and a spring is interposed between a
flange of the static plunger and the piston. The usable stroke of
the piston is limited to the extension of the piston skirt, which
must never completely leave the cylinder. This patent also
describes a piston formed by two parts that create between them a
path for the fluid to exit. The maximum useful stroke of the piston
is nevertheless limited by the axial length of the skirt integral
with the piston head.
U.S. Pat. No. 4,963,121 to Himura et al. also discloses a
tensioning device for a belt or chain drive mechanism that includes
a hollow piston element slidable inside a stationary cylinder. A
fluid chamber is defined between two reciprocally sliding tubular
elements of which one is fixed to the cylinder and the other moves
under the action of a fluid and of a spring, integrally with the
piston. The maximum useful outward stroke of the piston is defined
by the length of the skirt integral with the piston head.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, the tensioner
includes a cylinder, which may be in the form of a bore in the
tensioner housing, and a piston movable with respect to the
cylinder. The piston includes two or more reciprocally sliding
elements. A first distal element includes a piston head and a
skirt. A second proximal element, or plurality of proximal
elements, includes a skirt. A spring and pressurized fluid exert a
bias between the end of the cylinder and the piston head on the
distal element of the piston. Facing walls of the skirts of the
piston elements and the cylinder have reciprocal engaging means to
limit the movement of each with respect to the other.
The tensioner of the present invention allows the piston to extend
from the cylinder for a longer stroke than previous tensioners.
Yet, the axial measurement of the tensioner or axial length of the
tensioner when retracted is equal to previous tensioning
devices.
For a better understanding of these and other aspects and objects
of the invention, reference should be made to the following
detailed description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings,
FIG. 1 is a sectional view along a central axis of a
cylinder-piston assembly of a tensioning device according to the
invention, such as a plane substantially parallel to the drawing
sheet and through the device shown in FIG. 5, in a retracted
state.
FIG. 2 is a sectional view similar to FIG. 1 with the tensioning
device shown in a partially extended state.
FIG. 3 is a sectional view similar to the previous figures, with
the tensioning device shown in the position of maximum
extension.
FIG. 4 illustrates a tensioning device with an oscillating shoe
positioned on a chain drive of a timing system.
FIG. 5 illustrates a tensioning device with a translating shoe
positioned on a chain drive of a timing system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A tensioning device illustrated in the figures is indicated
generally by reference number 10.
The tensioning device 10 includes a body or cylinder 20 with a
hollow center or bore, and a piston or plunger 30 formed of a
plurality of elements. The piston includes at least two elements 31
and 32, respectively. The body or cylinder 20 has fixing tabs 21
for securing the tensioner to an engine body. The center of the
cylinder, or bore, forms an internal cylindrical chamber 22. The
chamber 22 communicates with a supply of pressurized fluid,
generally oil, through an opening 23, and a check valve 24, in a
manner well known and described in the prior art.
The piston 30 includes a first element or distal element 31 and a
second element or proximal element 32. The first element includes a
crown or piston head, 310, and a cylindrical skirt 311. The second,
proximal element 32 includes a cylindrical skirt 321. Between the
bottom of the cylindrical chamber 22 of the cylinder and the head
310 of the distal element a piston spring or pressure spring 40 is
interposed. The outer wall of the skirt 311 of the distal element
of the piston has a seat 312 for a piston ring 313, in an
intermediate position along the length of the skirt 311. The inner
surface of the piston element 32 has a groove 322 near the distal
end thereof, to allow widening or expansion of the piston ring 313.
Engagement of the piston ring 313 in the groove 322 prevents
further extension of the distal element 31 of the piston with
respect to the proximal element 32 of the piston.
The outer wall of the proximal element 32 of the piston has a seat
323 for a piston ring 324. In the proximity of the end the inner
face of the cylinder 20, a corresponding groove 202 is able to
receive the elastic ring 324 to stop further extension of the
element 32 of the piston from the cylinder.
The annular grooves or housings 322, 202 preferably have the
respective distal wall forming a steep step outwards (that is,
toward the right in FIG. 1) and the proximal wall gently sloping
inward, that is, toward the left in FIG. 1. The proximal element 32
of the piston 30 has a step 325 in its proximal part facing toward
the axis to form an abutment for distal element 31 in a retracted
position.
In the retracted or resting position illustrated in FIG. 1, the two
elements 31 and 32 of the piston 30 are in the retracted state,
i.e., the element 31 is completely or almost completely received
inside the cylinder 20. This position can coincide with the
initially set position of the tensioning device. The head 310 of
the device may be brought into contact with a shoe, generally an
oscillating shoe (FIG. 4) or a translating shoe (FIG. 5) which can
be pushed against chain C, or the like, to tension it. When fluid
is introduced through the opening 23 and the check valve 24 into
the chamber 22, the piston is biased out of the cylinder through
the action of the fluid and the spring 40. The bottom of the
chamber 22 of the cylinder and the head 310 of the distal element
31 of the piston are pushed apart by the spring. This causes the
element 31 to be extended (towards the right in FIG. 1) with
respect to the second element 32, and the element 32 to be extended
with respect to the cylinder 20. The position of the elements 31
and 32 with respect to each other and with respect to the cylinder
20 is determined by the balance of forces exerted by the pressure
of the fluid and the spring, on one hand, and the tension of the
chain on the other.
The extension of the piston elements is limited by engagement of
the piston ring 312 in the groove 322, and by engagement of the
piston ring 323 in the groove 202. The maximum extension position
is illustrated in FIG. 3. As can be seen from the figures, for
tensioning devices having a same axial length L, (FIG. 1), in the
retracted position, a conventional tensioning device could give a
maximum useful stroke L1 as shown in FIG. 2, while the new
tensioning device permits a useful stroke L2, marked in FIG. 3,
which is considerably greater than L1.
Those skilled in the art to which the invention pertains may make
modifications and other embodiments employing the principles of
this invention without departing from its spirit or essential
characteristics particularly upon considering the foregoing
teachings. The described embodiments are to be considered in all
respects only as illustrative and not restrictive and the scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. Consequently, while the
invention has been described with reference to particular
embodiments, modifications of structure, sequence, materials and
the like would be apparent to those skilled in the art, yet still
fall within the scope of the invention.
* * * * *